Superconducting Arcs

An essential ingredient for the production of Majorana fermions that can be used for quantum computing is the presence of topological superconductivity. As bulk topological superconductors remain elusive, the most promising approaches exploit proximity-induced superconductivity making systems fragile and difficult to realize. Weyl semimetals due to their intrinsic topology belong to potential candidates too, but search for Majorana fermions has always been connected with the superconductivity in the bulk, leaving the possibility of intrinsic superconductivity of the Fermi surface arcs themselves practically without attention, even from the theory side.Here, by means of angle-resolved photoemission spectroscopy and ab-initio calculations, we unambiguously identify topological Fermi arcs on two opposing surfaces of the non-centrosymmetric Weyl material PtBi2. We show that these states become superconducting at different temperatures around 10K. Remarkably, the corresponding coherencepeaks appear as the strongest and sharpest excitations ever detected by photoemission from solids, suggesting significant technological relevance. Our findings indicate that topological superconductivity in PtBi2 occurs exclusively at the surface, which not only makes it an ideal platform to host Majorana fermions, but may also lead to a unique quantum phase - an intrinsic topological SNS Josephson junction.Comment: 8 pages, 4 figures and Supplementary Informatio

The Initial Response to COVID-19 Disruptions for Older People with HIV in Ukraine

Ukraine imposed a COVID-19 lockdown in March 2020. From April to June 2020, we surveyed 123 older people with HIV (OPWH) by phone to assess their mental health, engagement in HIV and other healthcare, and substance use using standardised scales. Variables of key interest were symptoms of depression and symptoms of anxiety. Univariate and multivariable Firth logistic regression models were built to assess factors associated with: (1) symptoms of depression, and (2) symptoms of anxiety. Findings indicated high suicidal ideation (10.6%); 45.5% met the screening criteria for moderate to severe depression; and 35.0% met the criteria for generalised anxiety disorder (GAD). Independent correlates of having moderate to severe depression included being female (AOR: 2.83, 95%CI = 1.19–7.05), having concerns about potential barriers to HIV treatment (AOR: 8.90, 95%CI = 1.31–104.94), and active drug use (AOR: 34.53, 95%CI = 3.02–4885.85). Being female (AOR: 5.30, 95%CI = 2.16–14.30) and having concerns about potential barriers to HIV treatment (AOR: 5.33, 95%CI = 1.22–28.45) were independently correlated with GAD, and over half (58.5%) were willing to provide peer support to other OPWH. These results highlight the impact of the COVID-19 restrictions in Ukraine on mental health for OPWH and support the need to screen for psychiatric and substance use disorders, potentially using telehealth strategies